Appeal to reason here, OK?
"If you're living off the government dime then ..."
Let's go with that. The military lives off the government dime. People who collect Social Security live off the government dime. Then there's congress persons, all of the bureaucrats, the FBI, CIA, NSA, all of the contractors sucking on the hind tit of government, the scientists with grants, academia in some cases, etc.
I used to do government contracting for the DoD and I definitely had to subject to drug testing. In fact, if I tested positive for anything that I didn't have a prescription for, I could be in huge trouble. In fact, I couldn't even travel to a non-NATO country without notifying the US Government. So FBI, CIA, and NSA are covered by drug screening (in theory). I can't attest to congress critter, having never been a critter myself.
Why test just welfare recipients? You do know they don't have much in the way of resources, right?
I know they don't have much in the way of resources. That's why I feel like it's especially egregious if they use their meager resources on illicit drugs. And as I said, if we didn't cause drug prices to be artificially high, I think we would be much better off. We should just legalize the drugs. As long as they are illegal, I don't see anything wrong with the drug testing.
Also, the Constitution prohibits favoring one group over another without due process. Studies show that we don't even have probable cause !
The constitution doesn't guarantee welfare money. So there is, as far as I can tell, no constitutional protection against requiring drug screening for welfare eligibility. Now, I don't believe they should be using those drug screens for law enforcement. There would be a constitutional issue there. But welfare is only granted via legislation and therefore its rules and eligibility are subject to legislation also. I don't think the constitution plays a part at all. Otherwise, how can the government discriminate against drug users in employment? What is the difference? Of course, IANAL and YMMV.
If it were up to me, welfare recipients would be required to do X hours of community service per week, based on the stipend they received. Unfortunately for me (or fortunately for those who disagree with me) I don't get to make these rules.